Cell Fatty Acid Research Articles

Effects of 2,2′,5,5′-tetrachlorobiphenyl and biphenyl on cell membranes of Ralstonia eutropha H850

The effects of 2,2′,5,5′-tetrachlorobiphenyl (TeCB), a PCB congener, and biphenyl on the cytoplasmic membranes of Ralstonia eutropha H850 were investigated by measuring fluorescence polarization using 1,6-diphenyl-1,3,5-hexatriene (DPH) as the probe, and determining the cellular fatty acid compositions. TeCB significantly affected the membrane of R. eutropha H850 cells grown on fructose by decreasing DPH fluorescence polarization. In contrast, the membrane of cells grown on biphenyl showed a considerably less significant effect of TeCB on membrane polarization than in fructose-grown cells. An increase in the ratio of total saturated to unsaturated fatty acids in cells grown on biphenyl suggested less of a fluidizing effect of TeCB on membranes in those cells. When biphenyl-grown cells were transferred back to a fructose medium, they required 25 generations for the membrane polarization and fatty acid compositions of these cells to revert back to those of the initial fructose-grown cells. The re-adaptation to a change in temperature required only five generations to return to normal. These results show that biphenyl affects cells in more ways than simply fluidizing the cytoplasmic membrane.

Effects of 2,2',5,5'-tetrachlorobiphenyl and biphenyl on cell membranes of Ralstonia eutropha H850.

The effects of 2,2',5,5'-tetrachlorobiphenyl (TeCB), a PCB congener, and biphenyl on the cytoplasmic membranes of Ralstonia eutropha H850 were investigated by measuring fluorescence polarization using 1,6-diphenyl-1,3,5-hexatriene (DPH) as the probe, and determining the cellular fatty acid compositions. TeCB significantly affected the membrane of R. eutropha H850 cells grown on fructose by decreasing DPH fluorescence polarization. In contrast, the membrane of cells grown on biphenyl showed a considerably less significant effect of TeCB on membrane polarization than in fructose-grown cells. An increase in the ratio of total saturated to unsaturated fatty acids in cells grown on biphenyl suggested less of a fluidizing effect of TeCB on membranes in those cells. When biphenyl-grown cells were transferred back to a fructose medium, they required 25 generations for the membrane polarization and fatty acid compositions of these cells to revert back to those of the initial fructose-grown cells. The re-adaptation to a change in temperature required only five generations to return to normal. These results show that biphenyl affects cells in more ways than simply fluidizing the cytoplasmic membrane.

Effects of sodium chloride on the fatty acids composition in Boekelovia hooglandii (Ochromonadales, Chrysophyceae)

SUMMARY Composition of fatty acids in Boekelovia hooglandii Nicolai et Baas Becking (Chrysophyceae) was investigated as a function of salinity. It was confirmed by gas chromatography that the composition of fatty acids in cells cultured in a 50 mmol L−1 NaCl medium consisted of C14:0, C15:0, C16:0, C16:1, C18:0, C18:1, C18:2, C18:3, C18:4, C20:0, C20:4, C20:5, C22:5 and C22:6, in which C14:0, C16:0, C16:1, C18:4, C20:0, C20:5, C22:5 and C22:6 were main constituents. When the cells were cultured in a medium with different concentrations of NaCl ranging from 50 to 800 mmol L−1, the mole percentage of fatty acids such as C14:0, C16:0 and C16:1 decreased with increases in the salinity, while the mole percentage of highly polyunsaturated fatty acids such as C18:4, C20:5, C22:5 and C22:6 increased. When the cells were transferred from a 200 mmol L−1 NaCl medium to a 600 mmol L−1 NaCl medium, a decrease in mole percentage of C14:0, C16:0 and C16:1, and an increase in C18:4, C20:5, C22:5 and C22:6 were observed within 4 h. However, no change in the compositions of fatty acids was observed within 4 h when the cells were transferred from a 600 mmol L−1 NaCl medium to a 200 mmol L−1 NaCl one. The increase in the content of highly polyunsaturated fatty acids was considered to reflect the rapid response to upshock and to be the characteristic of salt tolerance in B. hooglandii.

Effect of exogenous sterols on the growth and fatty acid composition of the oomycetePythium debaryanum

Exogenous ergosterol and cholesterol were found to affect the growth and lipogenesis of the oomycete fungus Pythium debaryanum, which is unable to synthesize de novo steroid compounds. These sterols stimulated the growth of the fungus during its submerged cultivation in glucose-peptone medium. This was accompanied by the shortening of the lag phase, the lengthening of the period of active growth, and by a 3.7- or 4.3-fold increase in the maximum biomass in response to the addition of ergosterol or cholesterol, respectively. In the presence of ergosterol, the cellular content of polyenoic fatty acids increased, and the relative content of eicosapolyenoic fatty acids reached 31.4% of the total amount of fatty acids in cells. Conversely, cholesterol decreased the cellular content of polyenoic acids, and the relative content of eicosapolyenoic acids fell to 19.6% of the total amount of fatty acids. It may be inferred that exogenous sterols enhance the yield of pharmacologically active polyenoic acids because of the growth stimulation.

A highly CO2-tolerant diatom, Thalassiosira weissflogii H1, enriched from coastal sea, and its fatty acid composition

SUMMARY: A marine plankton-net sample containing 18 genera with 26 species of diatoms and one genus with two species of dinoflagellate collected from the surface water of Seto Inland Sea was used for an enrichment culture under bubbling 10% CO2 in air, and a 10% CO2-tolerant microalga was isolated and identified as Thalassiosira weissflogii H1. There was no significant difference between the growth rates and maximum growth yields of this diatom under bubbling air, 5% CO2 and 10% CO2, but the growth rate and maximum growth yield under 20% CO2 markedly decreased. The percentages of EPA and DHA for the total fatty acids in cells under 5–20% CO2 were lower than those under air. However, the ratios of EPA to algal cells – dry weight under 5% CO2, 10% CO2 and 20% CO2 were 0.76, 0.36 and 0.37 (% of dry weight), respectively, as compared with 0.18 under air. There was no significant difference in DHA contents (0.05 under air, 0.13 under 5% CO2, 0.05 under 10% CO2 and 0.09 under 20% CO2), with or without bubbling CO2. The polysaccharide content in the cells under 10% CO2 was higher than that in the cells under air. This study is the first report on a highly CO2-tolerant diatom.

Quantitation of the Mass of Fatty Acid Ethyl Esters Synthesized by Hep G2 Cells Incubated with Ethanol

Fatty acid ethyl esters (FAEE), esterification products of fatty acids and ethanol, have been increasingly implicated as mediators of ethanol-induced organ damage. The first goal of this study was to determine the mass of FAEE synthesized by Hep G2 cells exposed to a given dose of ethanol. The second goal was to determine whether all fatty acids in cells are equally available for FAEE synthesis. Hep G2 cells and essential fatty acid deficient Hep G2 cells (Hep G2-EFD) were used to study the synthesis of FAEE upon exposure to ethanol. A two-pool fatty acid model was created: (1) a "previously incorporated pool" formed by incubating the cells with 14C-labeled fatty acids for 24 hr; and (2) a "newly incorporated pool" formed by incubating cells with 3H-labeled fatty acids for 0.5 hr. The FAEE production from each pool was then determined. The total production of FAEE within 3 hr by Hep G2 cells in culture was 150 to 250 pmol/mg cell protein. The fatty acids most recently incorporated into the cells were preferred as substrates for FAEE synthesis because a higher percentage of fatty acids from the newly incorporated pool was used for FAEE synthesis than from the previously incorporated pool. Furthermore, a dose-response relationship was observed between the amount of fatty acid in the newly incorporated pool and FAEE production, but not between the amount of fatty acid in the previously incorporated pool and FAEE synthesis. Taken together, the results indicate that a relatively small amount of endogenously synthesized FAEE is generated from specific intracellular pools of fatty acid since not all fatty acids are equally available for FAEE synthesis. This indicates that if endogenous FAEE are toxic, they exert their toxic effect at very low intracellular FAEE concentrations.

Lipid storage compounds in marine bacteria

Forty psychrophile or psychrotrophic crude-oil-utilizing marine bacteria were investigated for their ability to accumulate lipid storage compounds in the cytoplasm during cultivation under nitrogen-limiting conditions. Most of them (73%) were able to accumulate specialized lipids like polyhydroxyalkanoic acids (PHA) while other lipids such as wax esters occurred in two isolates. Accumulation of PHA occurred predominantly at low temperatures (4–20 °C) as demonstrated for three isolates. Electron microscopy revealed polyphosphate inclusions occurring in two isolates in addition to PHA. Cells of the isolate Acinetobacter sp. 211 were able to synthesize and accumulate lipid inclusions during growth on acetate, ethanol, olive oil, hexadecanol and heptadecane. The composition of the lipid inclusions depended on the compounds provided as carbon source. Wax esters and acylglycerols occurred mainly during the cultivation on olive oil; in contrast, wax esters and free alcohols occurred during cultivation on hexadecanol. Total fatty acids in cells of the Acinetobacter sp. 211 amounted to 25% of the cellular dry weight in olive-oil-grown cells. Palmitic acid was the main fatty acid in the lipids when the cells were cultivated on acetate or ethanol (44% and 32% of total fatty acids respectively). In contrast, fatty acids occurring in the lipids during cultivation on hexadecanol, heptadecane or olive oil were related to the carbon source. The fatty acids present in the accumulated lipids consisted predominantly of saturated and unsaturated straight-chain fatty acids with a chain length ranging from 12 to 18 carbon atoms. Analysis of the lipid-granule-associated proteins in cells of Acinetobacter sp. 211 revealed a protein of 39 kDa as the predominant protein species.

N-3 but not N-6 fatty acids reduce the expression of the combined adhesion and scavenger receptor CD36 in human monocytic cells.

CD36, a multifunctional adhesion receptor e.g. for thrombospondin and collagen, as well as a scavenger receptor for oxidized low density lipoprotein, is expressed e.g. on platelets and monocytes. By this dual role it might be involved in early steps of atherosclerosis like the recruitment of monocytes and formation of foam cells. We therefore studied the effects of n-3 fatty acids on CD36 expression in human monocytic cells. Incorporation of eicosapentaenoic acid (EPA, C20:5n-3) and docosahexaenoic acid (DHA, C22:6n-3) into cellular phospholipids resulted in a significant reduction of CD36 expression at the mRNA and protein level, whereas arachidonic acid (AA, C20: 4n-6) and linoleic acid (LA, C18:2n-6) tended to increase CD36 expression compared to the control. This specific down-regulation of CD36 by n-3 fatty acids in cells involved in the initiation and progression of atherogenesis and inflammation, represents a further mechanism that may contribute to the beneficial effects of n-3 polyunsaturated fatty acids (PUFA) in these disorders.

Fatty acids. Biochemistry to clinical significance.

Fatty acids are a major source of lipids in the diet. Dietary fatty acids are able to significantly influence the concentration of serum cholesterol and thereby influence the risk of atherosclerosis. This brief review on fatty acids will present information on the structure and nomenclature of fatty acids, the metabolic pathways for fatty acids in cells, and the influence of dietary fatty acids on serum cholesterol levels.

Fatty acid uptake and metabolism in CaCo-2 cells: eicosapentaenoic acid (20:5( n − 3)) and oleic acid (18:1( n − 9)) presented in association with micelles or albumin

In vivo, long-chain fatty acids are incorporated into bile salt micelles, which solubilize the hydrophobic fatty acids before they are transported across the unstirred water layer to the intestinal brush border membrane. In the present study we have used CaCo-2 cells, cultured on filter membranes as a model of human enterocytes, and compared presentation of fatty acids bound to albumin with a micellar form. Absorption of eicosapentaenoic acid and oleic acid from micellar solutions was 4-times faster than from fatty acid-albumin complexes after 5 h incubation, and resulted in a corresponding increase in triacylglycerol synthesis and secretion. Mass determination of newly synthesized, cell-associated triacylglycerol after 5 h incubation, indicated a 5-fold increase in cells exposed to a micellar solution versus albumin-complexed fatty acids. A 2-fold larger fraction of the absorbed fatty acids was incorporated into triacylglycerol than into phospholipids when the fatty acids were presented as micelles. Analysis by resistive pulse technique showed that secreted lipoproteins of density less than 1.006 g/ml were in the same size-range as chylomicrons derived from human plasma. In spite of an increased amount of secreted triacylglycerol from cells supplemented with micellar fatty acids, there was no increase in the mean size of these particles. Synthesis and secretion of triacylglycerol in cells exposed to eicosapentaenoic acid and oleic acid were similar regardless of whether the fatty acids were presented to the cells associated with albumin or micelles, although the total amount of triacylglycerol synthesized and secreted was highest with micelles. When incubating CaCo-2 monolayers with eicosapentaenoic acid or oleic acid bound to albumin, a similar amount of radioactivity was released as CO 2 and acid soluble products into the medium with less than 3% of the lipids being oxidized after 5 h of incubation. The oxidation rate of fatty acids in cells incubated with micelles was increased 40 to 100%. In conclusion, micellar fatty acids are absorbed, metabolized and influence secretion of lipoprotein particles to a higher extent than albumin-bound fatty acids in CaCo-2 cells, and there is no major difference between eicosapentaenoic acid and oleic acid.

Effect of temperature on ethanol productivity and resistance of cryophilic wine yeasts.

Effects of incubation temperature and ethanol concentration on cell viability of two strains of cryophilic wine yeasts YM-84 and YM-126 were compared with those of mesophilic wine yeasts W3 and OC-2. The cryophilic wine yeasts showed certain cell viability in the presence of 10% ethanol at 8°C, the same as the mesophilic wine yeasts. At 25°C, however, viable cell numbers of these cryophilic wine yeasts were decreased, and this tendency became more marked with the presence of ethanol. Comparison of the composition of fatty acid in cells, YM-84 and YM-126 showed higher proportions of myristic acid to fatty acid, in addition to higher ratios of C16 fatty acids to C18 fatty acids. These phenomena suggest that these strains have different adaptation mechanisms against temperatures. Five strains of cryophilic wine yeasts selected in our culture collection showed the same fermentation velocity at the low temperature of 7°C as did YM-84 and YM-126, and at 28°C their ethanol yields were reduced. From these results, it can be concluded that good fermentability at low temperatures accompanied by production of low amounts of ethanol at intermediate temperatures is one of the fermentation characteristics observed among cryophilic wine yeasts.

Effects of trans fatty acids on lipid accumulation in 3T3-L1 cells.

Previous work had shown that dietary trans fatty acids (tFA) resulted in decreased fat deposition in adipose tissue. This study was conducted to see if tFA influence lipid accumulation in Swiss mouse fibroblast 3T3-L1 cells, which are widely used as an adipocyte model. Cells were cultured in the presence of experimental or control growth media supplemented with fatty acids complexed to bovine serum albumin. Fatty acid compositions of experimental and control growth media were similar except that the octadecenoates in the control growth media were cis fatty acids, whereas those in the experimental media contained both cis and trans fatty acids. Cell-conditioned media and cellular lipids at the preadipocyte and differentiating adipocyte stages were analyzed. At both stages of development, less fat accumulated in cells cultured in the presence of tFA, due primarily to a decrease in the nonpolar lipid content of cells exposed to tFA, and linoleate to arachidonate ratios were higher in cells supplemented with tFA. Calculations comparing sums of saturated and monounsaturated fatty acids in cells at the differentiating adipocyte stage suggested that tFA may have replaced monounsaturated fatty acids in the nonpolar lipid fraction and saturated fatty acids in the polar lipid fraction. The results of these studies are in good agreement with the in vivo effects of tFA seen in previous work with mouse adipose tissue. It was concluded that the 3T3-L1 in vitro model is an appropriate system for further studies of tFA and lipid metabolism in adipose tissue.

Fatty acids from 28 marine microalgae

Fatty acid (FA) compositions and C/N ratios of 28 marine microalgae from nine taxonomic classes were examined. A combination of several criteria was selected to discriminate taxonomic classes: 16:4 (n-1), 20:5 (n-3), 22:6(n-3), C 18 polyunsaturated FA (PUFA), C 20)PUFA, C 22PUFA, 16:1(n-7)/I6:0, C 16FA/C 18FA, C 16PUFA/ C 18PUFA, 18:5(n-3)/18:3(n-3). Results expressed in terms of relative abundance (per cent of total fatty acids) and absolute abundance (ng FA mg C −1 and pg FA cell −1) led to different interpretations concerning the nutritional value of the different species as food for organisms in culture or in the natural environment.

An in vitro model for essential fatty acid deficiency: HepG2 cells permanently maintained in lipid-free medium.

A stable essential fatty acid-deficient cell type, known as HepG2-EFD, was derived from the lipoprotein-producing human hepatoma cell line HepG2. These cells are particularly useful for quantitative studies involving essential fatty acids (n-6 and n-3 fatty acids) in secreted lipoproteins. Radiolabeled essential fatty acids can be delivered to these cells without altering the specific activity of the fatty acids, since the deficient cells contain no endogenous essential fatty acids. Using these cells, radioactivity data (dpm) from metabolic studies can be converted directly to mass, and masses as low as a few pmoles can be accurately measured. HepG2-EFD cell cultures were established by growing HepG2 cells in medium containing delipidated serum. After 10 days of growth in delipidated medium, HepG2 cells were completely depleted of all essential fatty acids. Compensatory increases in nonessential fatty acids (n-9 and n-7 fatty acids) including 20:3n-9 (the Mead acid), which is the hallmark fatty acid of essential fatty acid deficiency, were also observed in HepG2-EFD cells. Despite the lack of exogenous fatty acids in the medium and the lack of essential fatty acids in the cells, export of very low density lipoprotein (VLDL)-associated apolipoprotein B by HepG2-EFD was the same as observed for parent HepG2 cells. However, the activity of beta-oxidation of fatty acids in HepG2-EFD cells was much lower than in the parent cell line.(ABSTRACT TRUNCATED AT 250 WORDS)

The leakage of fatty acid binding protein from cultured myocardial cells during hypoxia

Fatty-acid binding protein (FABP) is thought to play an important role as a carrier protein of fatty acids in cells. It may leak from damaged cells, because its molecular weight is low (mol wt 14000) and it accounts for several percent of soluble protein. In this experiment we attempted to use FABP as a marker of cell injury under hypoxia in cultured myocytes. Newborn-rat myocytes were incubated under hypoxic treatment for 6 hours, and then the releases of FABP and CPK were measured. The cell-death ratio during hypoxygenation increased from 4 hours and rose to 80% at 6 hours, but it was only 8% under aerobic conditions. FABP in medium was detected at 1 hour, and rapidly increased and reached a plateau at 4 hours. On the other hand, CPK in medium was negligible during the 3 hours, then slightly increased. Ca antagonists and a beta 1-adrenergic blocking agent inhibited the release of FABP and prevented cell death. But the alpha 1-adrenergic blocking agent had little effect on preventing FABP leakage and cell death. These results show that FABP is of use as a marker of myocardial cell injury and revealed that the Ca antagonist and beta 1-adrenergic blocking agent are useful drugs for the protection of myocardial cell injury in hypoxia.

Retroconversion and δ4 desaturation of docosatetraenoate (22:4( n−6)) and docosapentaenoate (22:5( n−3)) by human cells in culture

This study has investigated the metabolic modification of [3- 14C]docosatetraenoate (22:4( n−6)) and [3- 14C]docosapentaenoate (22:5( n−3)) by human cells in culture. Fetal skin fibroblasts converted as much as 20% of the incoporated [ 14 C]22:4(n−6) to [ 14 C]20:4(n−6) within 6 h and 41% within 48 h. Retroconversion of incorporated [ 14 C]22:5(n−3) was less than 13% at all time points. Chain shortening of [ 14 C]22:4(n−6) was also 2–6-fold greater than that of [ 14 C]22:5(n−3) in retinoblastoma and vascular endothelial cells. Fibroblasts, vascular endothelial cells and retinoblastoma cells all elongated substantially more [ 14C]eicosapentaenoate than [ 14C]arachidonate to the respective C 22 fatty acids. Within 3–4 days, fibroblasts incubated with either [ 14 C]20:5(n−3) or [ 14 C]22:5(n−3) had the same ratio of radiolabeled C 22:C 20 fatty acids in cellular glycerolipids. By contrast, the cells incubated with [ 14 C]22:4(n−6) or [ 14 C]22:4(n−6) did not reach a common C 22/C 20 equilibrium by 5 days. Although fibroblasts were found to desaturate [ 14 C]22:5(n−3) , a substantial lag time was observed; [ 14 C]22:5(n−3) was 2% at 48h and 20% at 96h. By contrast, synthesis of [ 14 C]22:6(n−3) by retinoblastoma cells was 51% within 6 h and > 90% at 96 h. Desaturation of [ 14 C]22:4(n−6) was observed in retinoblastoma cells, but not in fibroblasts. These results thus suggest that the ratio of C 22C 20 polyunsaturated fatty acids in cells is regulated by the relative rates of retroconversion and chain elongation, with the net effect of the two processes favoring C 20 for n−6 and C 22 for the n−3 fatty acids. Furthermore, although fibroblasts desaturate [ 14 C]22:5(n−3) , the process appears to be qualitatively different from that of retinoblastoma cells.

A trans-unsaturated fatty acid in a psychrophilic bacterium, Vibrio sp. strain ABE-1

A high level of a trans-unsaturated fatty acid was found in the phospholipids of a psychrophilic bacterium, Vibrio sp. strain ABE-1. This fatty acid was identified as 9-trans-hexadecenoic acid (C16:19t) by gas-liquid chromatography and infrared absorption spectrometry. C16:1(9)t accounted for less than 1% of the total fatty acids in cells grown at 5 degrees C and reached 12% of the total at 20 degrees C. We suggest that the increase in the level of the trans-unsaturated fatty acid is related to the high growth rate of this bacterium at elevated temperatures. Possible biological roles of the trans-unsaturated fatty acid in the adaptation of the microorganism to the ambient temperature are discussed.

Polyunsaturated fatty acid-induced cytotoxicity against tumor cells and its relationship to lipid peroxidation.

The contribution of lipid peroxidation to the killing of human breast cancer cells by gamma-linolenate (GLA) was examined. Other fatty acids of different cytotoxic potential containing 2, 4, 5, and 6 double bonds were also tested for comparison. It was found that the cytotoxic potential varied with the ability of the fatty acids to stimulate the production of superoxide radicals. Neither hydrogen peroxide nor hydroxy radicals are significantly involved in cell killing. As nonspecific indicators of lipid peroxidation, measurements of the loss of unsaturated fatty acid in the phospholipids together with the generation of hydroperoxide breakdown products were done with the use of the thiobarbituric acid test. The results of these experiments showed that the effectiveness of a given fatty acid in killing cancer cells correlated with the intracellular thiobarbituric acid-reactive material (TBARM) content: GLA and arachidonate with 3 and 4 double bonds generated the most TBARM and were the most cytotoxic fatty acids, whereas docosahexaenoate with 6 double bonds was the least effective either in raising TBARM or in killing the malignant cells. Iron and copper accelerated the rate of cell death, whereas antioxidants such as vitamin E and butylated hydroxyanisole inhibited the effect of GLA dose dependently. Indomethacin, an inhibitor of endoperoxide formation, did not reduce either cell kill or TBARM amounts. In contrast, the addition of vitamin E acetate to the cancer cell cultures challenged with eicosapentaenoate reduced both cell killing and TBARM content. These results suggest that the effectiveness of a given fatty acid in killing cancer cells correlated with the extent of lipid peroxidation of the added fatty acid in the cells.

Possible involvement of acetyl coenzyme A carboxylase as well as fatty acid synthetase in the temperature-controlled synthesis of fatty acids in Saccharomyces cerevisiae.

Fatty acid synthetase (FAS) preparations from Saccharomyces cerevisiae cells grown at either 35 or 10 degrees C produced the same products at different temperatures and showed quite similar temperature-dependencies in Arrhenius plots, with break points at 25 degrees C. This break point does not appear to reflect a phase transition of phospholipids present in the purified FAS preparations but rather is associated with protein conformational changes. S. cerevisiae cells grown at 35 degrees C and then shifted to 10 degrees C produced fatty acids with a shorter average chain length than those fatty acids synthesized at 10 degrees C by cells already adapted to 10 degrees C (hyper response). Acetyl-CoA carboxylase activity was relatively higher in the cells grown at 35 degrees C than in the cells grown at 10 degrees C; moreover, fatty acids with longer average chain lengths were synthesized in vitro at higher malonyl-CoA concentrations, which was consistent with the difference in the average chain lengths of newly synthesized fatty acids in cells grown at 35 and 10 degrees C. However, the activity levels of acetyl-CoA carboxylase and fatty acid synthetase alone did not account for the hyper response phenomena.

Metabolism of Tween-Fatty Acid Esters by Cultured Soybean Cells

Uptake of Tween-fatty acid esters and incorporation of the fatty acids into lipids by soybean (Glycine max [L.] Merr.) suspension cultures was investigated, together with subsequent turnover of the incorporated fatty acids and associated changes in endogenous fatty acid synthesis. Tween uptake was saturable, and fatty acids were rapidly transferred from Tweens to all acylated lipids. Patterns of incorporation into glycerolipids were similar in cells treated with Tweens carrying [1-(14)C]-fatty acids and in cells treated with [1-(14)C]acetate, indicating that exogenous fatty acids were used for glycerolipid synthesis essentially as if they had been made by the cell. In Tween-treated cells neutral lipids (which include Tweens) initially accounted for the majority of lipid radioactivity. Radioactivity was then rapidly transferred to glycerolipids. A transient pool of free fatty acids accounting for up to 10% of lipid radioactivity was observed. This was consistent with the hypothesis that fatty acids are transferred from Tweens to lipids by deacylation of the Tweens, creating a pool of free fatty acids which are then used for lipid synthesis. Sterols were only slightly labeled in cells treated with Tweens, but accounted for nearly 50% of lipid radioactivity in cells treated with acetate. This suggested very little degradation and reutilization of the radioactive fatty acids in cells treated with Tweens. In cells treated with either [1-(14)C]acetate or Tween-[1-(14)C]-18:1, 70% of the initial fatty acid radioactivity remained in fatty acids after a 100 hour chase. By contrast, fatty acids not normally present disappeared more rapidly, suggesting differential treatment of such fatty acids compared with those normally present. Cells which had incorporated large amounts of exogenous fatty acids altered fatty acid synthesis in three distinct ways: (a) amounts of [1-(14)C]acetate incorporated into fatty acids were reduced; (b) cells incorporating exogenous unsaturated fatty acids increased the proportion of [1-(14)C]acetate partitioned into saturated fatty acids, while the converse was true of cells which had incorporated exogenous saturated fatty acids; (c) desaturation of 18:1 to 18:2 and 18:3 was reduced in cells which had incorporated unsaturated fatty acids. These results suggest that Tween-fatty acid esters will be useful for supplying fatty acids to cells for a variety of studies related to fatty acid or membrane metabolism.